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Posterior Mediastinal Masses

Neurogenic Tumors

            Peripheral nerve origin

                        • Neurofibromas

                        • Neurilemomas (Schwannomas)

            Sympathetic nerve origin

                        • Ganglioneuromas—usually benign

                        • Neuroblastomas—usually malignant

                        • Sympathicoblastomas—usually malignant

            Paraganglionic cells

                        • Pheochromocytoma

                        • Chemodactomas (paragangliomas)—benign or malignant  

• Posterior mediastinum is bordered anteriorly by the pericardium and posteriorly by the anterior border of the spine, so that the paravertebral gutters are technically excluded from the posterior mediastinum but for practical purposes are considered part of it

• Contains the descending aorta, esophagus, thoracic duct, vagus nerves and nodes

• About 30% of posterior mediastinal masses are malignant

• Nerve sheath tumors are the most common and are usually benign; neoplasms which arise from nerve elements other than the sheath are usually malignant

• In adults, neurofibroma and neurilemomas (Schwannomas) are most common
  

• Neurofibroma contains Schwann cells plus nerve cells; occur in 3rd or 4th decade
  

• Schwannoma derived from sheath of Schwann without nerve cell

• In children, ganglioneuroma and neuroblastoma are most common

• Ganglioneuroma– benign tumor

• Neuroblastoma–very malignant undifferentiated round cell lesion from sympathetic ganglion usually under age 10

o      Produces “ iron-filings” appearance to sutures in the skull infiltrated with tumor

• Calcification in a posterior mediastinal mass points to a neural tumor in a kid rather than a met from somewhere else

• Posterior mediastinal neurofibromas are only rarely associated with neurofibromatosis

• Most have no symptoms

X-ray

• Both benign and malignant tumors may erode ribs

• They may enlarge the neural foramina (dumbbell shaped lesion)

• Scalloping of posterior vertebral bodies may occur

• They may produce a scoliosis

• Pleural effusion may occur with benign as well as malignant neural tumor

Other posterior mediastinal masses  

• Paraspinal abscess from TB – look for destruction of two contiguous endplates plus narrowing of the intervening disc space

• Neurenteric cysts may have associated hemivertebra

• Extramedullary hematopoiesis should be associated with splenomegaly and sometimes widening of the ribs

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